In the fabrication of integrated circuits, various layers of the same or different materials are used. For example, during the formation of semiconductor devices, such as dynamic random access memories (DRAMs), static random access memories (SRAMs), ferroelectric (FE) memories, etc., a variety of conductive and non-conductive materials are used in the formation of storage cell capacitors and also may be used in interconnection structures, e.g., conductive layers of contact holes, vias, etc.
These materials are typically supplied in a gas phase conducive to the formation of a film on a surface. When supplied in the gas phase, many of these materials may become toxic or otherwise harmful to health. As a result, it may be important to monitor where these materials are found and the concentrations in which they are found. Furthermore, because the effects may be cumulative, i.e., repeated exposure to low levels of the selected materials may be additive, it may be important to provide sensors and detection methods that are capable of measuring for cumulative exposure levels in addition to real-time exposure.
Semiconductor device manufacturing is one example of an environment in which the monitoring of exposure to potentially harmful materials can be advantageous. For example, various metals, metallic compounds, metal oxides, etc. are used to manufacture various structures used in semiconductor devices. A number of these materials may pose health risks based on exposure to the materials in the gas phase.
For example, ruthenium oxide and ruthenium have recently been employed in semiconductor devices because these materials are electrically conductive, conducive to conformal deposition, and they are easily etched. For example, the article entitled, “(Ba,Sr)TiO3 Films Prepared by Liquid Source Chemical Vapor Deposition on Ru Electrodes,” by Kawahara et al., Jpn. J. Appl. Phys., Vol. 35 (1996), Part 1, No. 9B (September 1996), pp. 4880-4885, describes the use of ruthenium and ruthenium oxide for forming electrodes in conjunction with high dielectric constant materials. It is, however, known that gaseous ruthenium tetraoxide (RuO4) is toxic at very low levels, e.g., about 1 part per billion (ppb). Monitoring of exposure to ruthenium tetraoxide is, therefore, both important due to its toxicity and difficult due to the low exposure levels at which the toxicity becomes an issue.
For example, many detection systems or procedures for many different gas phase materials rely on chemically sensitive tapes. Stains are produced due to chemical reactions occurring on the tapes in response to chemical exposure and those stains can then be detected. Problems with such tapes may, however, include sensitivity to different chemicals.
With respect to ruthenium tetraoxide, some useful chemically sensitive tapes are also sensitive to other chemicals such as oxidizing agents. As a result, the tapes typically cannot be used to accurately detect exposure to ruthenium oxide. Other tapes may detect ruthenium oxide, but could not be used to accurately detect at desired exposure levels.